CN111527242B

CN111527242B - Method for determining surface temperature

Info

Publication number: CN111527242B
Application number: CN201780097489.0A
Authority: CN
Inventors: O·赛法特; S·佐梅劳尔; M·温泽伊斯
Original assignee: Wacker Chemie AG
Current assignee: Wacker Chemie AG
Priority date: 2017-12-05
Filing date: 2017-12-05
Publication date: 2021-09-07
Anticipated expiration: 2037-12-05
Also published as: TW201925769A; EP3684967B1; JP2021505880A; CN111527242A; JP6984018B2; KR102399202B1; US11515184B2; EP3684967A1; TWI690705B; KR20200074183A; US20200373177A1; WO2019110091A1

Abstract

The subject of the invention is a method for determining the surface temperature of at least one silicon rod in a chemical vapor deposition reactor during a deposition process, wherein a measuring device a determines the surface temperature in a measuring region provided on the silicon rod and a measuring device B determines continuously or discontinuously at least one diameter of the silicon rod and/or at least one diameter of at least one further silicon rod arranged in the reactor, the size and/or position of the measuring region being adapted depending on the determined diameter or diameters. Another subject of the invention is a device for determining the temperature of a surface and a reactor comprising such a device.

Description

Method for determining surface temperature

The invention relates to a method for determining the surface temperature of at least one silicon rod in a chemical vapor deposition reactor in a deposition process. The invention also relates to a device for determining the temperature of a surface, and to a reactor comprising such a device.

Polycrystalline silicon (polysilicon) is used as a raw material for producing single crystal silicon, for example, by crucible pulling (Czochralski process) or zone melting (floating zone process). Single crystal silicon can be sawed into wafers and, after many other processing steps, can be used in the semiconductor industry to manufacture electronic components (chips).

In addition, polycrystalline silicon is required for producing polycrystalline silicon (polycrystalline silicon) by, for example, a block casting process. Polycrystalline silicon obtained in bulk form can be used to fabricate solar cells. This is typically done by sawing a silicon block into rectangular wafers.

Polycrystalline silicon is typically produced by the Siemens process (chemical vapor deposition process). In this process, a filament rod (slim rod) of silicon is heated by direct passage of an electric current in a bell-shaped reactor (Siemens reactor), and a reaction gas containing a silicon-containing component and hydrogen is introduced. The silicon-containing component is typically monosilane (SiH)₄) Or of general composition SiH_nX_4-n(n ═ 0, 1, 2, 3; X ═ Cl, Br, I). The customary constituents here are chlorosilanes or chlorosilane mixtures, usually trichlorosilane (SiHCl)₃TCS). Mainly used is SiH₄Or SiHCl₃With hydrogen. The construction of a typical Siemens reactor is described, for example, in EP 2077252 a 2.

The reactor floor typically houses electrodes that receive the slim rods. Typically, two slim rods are each connected by a bridge to form a pair of slim rods or U-shaped rods (a pair of slim rods having an inverted U-shape), which form a circuit through the electrodes. The surface temperature of the filament rod is typically above 1000 ℃. These temperatures lead to decomposition of the silicon-containing component of the reaction gas and elemental silicon is deposited from the vapor phase onto the rod surface in the form of polycrystalline silicon (chemical vapor deposition, CVD). This results in an increase in the diameter of the slim rod. When the specified diameter is reached, deposition is usually stopped and the resulting U-shaped silicon rod is discharged. After removal of the bridge, a substantially cylindrical silicon rod is obtained.

The surface temperature of the silicon rod is an important influencing parameter, which is usually monitored during the deposition and can be adjusted by varying the passage of the current. In principle, the heat flow out of the silicon rod increases in proportion to the deposition time due to the increase in the diameter and thus the surface area of the silicon rod. Therefore, during deposition, it is often necessary to adapt the current intensity. Too high a surface temperature leads in principle to excessive formation of silicon dust, while too low a surface temperature leads to delayed deposition or no further deposition at all. Furthermore, the surface temperature determines the surface properties of the silicon rod and thus the quality of the silicon rod. Higher temperatures do generally lead to faster growth of the silicon rods, but as the temperature increases, the phenomenon of surface irregularities increases.

One known technique for measuring the surface temperature of silicon rods is the use of a pyrometer, for example a radiation pyrometer. In general, pyrometers measure the temperature of a measurement point on a surface based on the intensity of radiation emitted at a particular wavelength or within a particular range of wavelengths. Due to the heat inside the reactor, measurements are in principle made from outside the reactor, wherein the radiation is detected through observation windows installed in the reactor wall. In order to ensure uninterrupted passage of radiation, the observation window is usually equipped with special optics.

A general problem associated with determining the temperature of only one measuring point is the surface properties of the polycrystalline silicon rod. Ideal measurement results can only be achieved on flat surfaces. However, in practice, grooves and protrusions may appear on the surface of the silicon rod, and their surface temperatures may be greatly different.

EP 2391581B 1 discloses a method for measuring the diameter and the surface temperature of silicon rods. In the method, temperature measurements are taken over time using a pyrometer which is horizontally rotatable about an axis of rotation parallel to the longitudinal axis of the silicon rod, and at the same time the growth in thickness is measured by horizontal rotation. Thus, a plurality of temperature measurements are made on a horizontal line.

In the case of a rotatable pyrometer, it may occur that further silicon rods in the reactor enter the light path between the pyrometer and the silicon rod under test. In addition, the temperature of the inner reactor wall can be detected. In order to exclude such interference signals, a procedure is required for determining whether a temperature is detected on or in the vicinity of the silicon rod under test according to a predetermined threshold temperature. This threshold method is more susceptible to interference. For example, fluctuations in the air flow may lead to measurement errors. Furthermore, it is often difficult to distinguish the temperatures from two bars mounted one above the other, which rotate. The determined diameter may be distorted accordingly. One complicating factor is that during deposition, the diameter of the polysilicon rod increases, thus altering the characteristic area of the temperature measurement. Also, as the focal point changes, the distance between the pyrometer and the rod surface decreases. Another challenge in measuring surface temperature is the side area of the silicon rod. In these regions it is often not possible to reliably capture the temperature, since only a small portion of the radiation emitted in these regions will hit the detector of the pyrometer.

EP 2732067B 1 discloses a method for monitoring the surface temperature of silicon rods in a CVD reactor by recording images of the reactor interior through an observation window using an image capture device (digital camera or CCD sensor). The temperature is determined by pixel analysis in a target area of constant size in the image. The radiation intensity of the silicon rod, and thus the temperature, is determined, where appropriate, by comparing the radiation intensity of the image with a reference image. Furthermore, based on the pixel analysis (transition from light pixels to dark pixels), the outer edge of the silicon rod may be determined. From these, the diameter can be calculated and the position of the target area specified.

A problem may arise when using only one image capturing device for determining the surface temperature and the rod diameter, in particular when stacking two silicon rods. Since the rods typically have approximately the same temperature, in some cases they may be detected as one rod and, therefore, the calculated diameter may be too large. If the area to be analyzed for temperature is located according to diameter, it may be the case that a curved bar edge is detected in the overlap area, thereby distorting the temperature analysis. In addition, the measurement region having a constant size in area does not take into account the curvature of the rod, which becomes smaller as the diameter of the silicon rod increases.

It is an object of the present invention to provide a method for measuring the surface temperature of silicon rods during operation of a deposition reactor, which method overcomes the disadvantages known in the prior art.

This object is achieved by a method for determining the surface temperature of at least one silicon rod in a chemical vapor deposition reactor during a deposition process, wherein a measuring device a determines the surface temperature in a measuring region provided on the silicon rod and a measuring device B determines continuously or discontinuously at least one diameter of the silicon rod and/or at least one diameter of at least one further silicon rod arranged in the reactor. The size and/or position of the measurement region on the silicon rod is adapted or defined here as a function of the determined diameter or diameters.

The method preferably comprises the steps of:

a) determining at least one diameter of at least one silicon rod with measuring device B;

b) determining the size and/or position of a measurement area on the silicon rod on the basis of the diameter determined in step a);

c) measuring the surface temperature in the measurement area with a measuring device a;

d) continuously or discontinuously repeating steps a), b) and c) and continuously or discontinuously adapting the size and/or position of the measurement region to the diameter of the silicon rod.

The use of two separate measuring devices a and B makes it possible in particular to determine the diameter of the silicon rod and its surface temperature without interruption. The measuring device can advantageously be arranged in such a way that the problem of overlapping of the individual measuring regions by other silicon rods is eliminated. The dynamic adaptation of the size of the measuring zone to the determined diameter of the rod takes directly into account that the curvature of the rod changes with increasing diameter. In addition, the measuring region can be kept particularly large in this way. As a result, the temperature difference on the rod surface caused by the surface structure can be compensated more effectively, so that the measurement result is not distorted. By dynamically adapting the position of the measurement region on the silicon rod, it can be ensured that the measurement region maintains a constant distance from one or both edges of the silicon rod. In particular, the measurement region may be positioned centrally between the bar edges, thereby eliminating side regions that often lead to inaccurate measurement results.

The vapor deposition reactor is more particularly a Siemens reactor. The number of silicon rods or silicon rod pairs arranged in the reactor is generally of no importance for the implementation of the process according to the invention. Typical examples of the number of silicon rods in the reactor are 36(18 pairs of rods), 48(24 pairs of rods) or 54(27 pairs of rods). The silicon rod can be considered approximately cylindrical. The slim rods may likewise be cylindrical, but may also be of other geometries. It may further be assumed that the surface temperature and the diameter of all silicon rods in the reactor are substantially the same, in particular when corresponding measurements are compared at the same rod height, e.g. in the middle of the rod. This approximation is reasonable because the design of modern Siemens reactors ensures the greatest degree of deposition uniformity, i.e. produces silicon rods of the same quality and shape. This is achieved by a uniform gas flow in the reactor, in particular a substantially symmetrical arrangement of the rods. The rod or rods determining the temperature and diameter are generally independent of the number of silicon rods arranged in the reactor. Furthermore, dynamically adapting the temperature measurement region for the growth of the silicon rod has the advantage that any temperature differences occurring are averaged out.

The surface temperature and/or diameter are preferably measured from outside the reactor through a viewing window. In this case, the measuring devices a and B are arranged in particular at different positions, each in front of the observation window. Preferably, however, the measuring means are located at the same height, it being irrelevant whether the measuring means are located at a height such as the centre of the stick or at a height of the upper or lower third of the stick. For example, the measuring device a may be arranged on the opposite side of the generally bell-shaped reactor to the measuring device B. The measuring devices are preferably placed alongside one another (in the circumferential direction of the reactor) in front of the observation window. They may also be placed alongside one another or one above the other, in front of a common viewing window.

Continuous repetition refers in particular to capturing the diameter, thus dynamically adapting the measurement area and/or its position in real time throughout the deposition process. In the case of discontinuous repetition, the capturing is performed at specified time intervals, for example every minute or every hour.

The measuring device B preferably comprises a camera, more particularly a digital camera or a CCD camera. The measuring device B is preferably such a camera. The diameter is determined by image processing, in particular digital image processing, of the image or image details of the interior of the reactor produced by the measuring device B. Provision may also be made for video to be generated, in which case preferably a single image from the video is subjected to image processing.

The image processing can be carried out by means of an analog or digital image processing unit, which is preferably part of the measuring device B. More particularly, it may relate to computer software. The image processing unit may also be a separate device connected to the measuring device B.

The diameter can be determined by selecting the focal point of the camera such that the width of the at least one silicon rod is visible in front of the inner wall of the reactor. In general, on the image obtained in this way, the silicon rod appears bright against the inner reactor wall, which appears dark in the background. Then, through pixel analysis, the image processing unit is able to identify the left contour (edge) and the right contour (edge) of the silicon rod and determine the distance between them. The camera is usually calibrated so that the image it records corresponds in its width to a certain distance in the circumferential direction on the inner wall of the reactor. The geometry of the reactor, in particular the circumference of the reactor at the camera level, is fundamental knowledge. The position of the silicon rod and thus its distance from the inner wall of the reactor and from the camera are likewise generally known. By correlating the known spacing or distance from the reactor configuration, the distance between the left and right profiles of the silicon rods can then be used to calculate the rod diameter. The focus of the camera may also be chosen such that in front of the inner wall of the reactor the entire width of two or more, more particularly two or three, silicon rods can be seen. The measurement principle remains unchanged.

It is also possible in principle to use the image obtained to measure the distance between two adjacent rods in front of the reactor wall and to calculate their diameter from this measurement, in particular by triangulation. In the case of this variant, the two adjacent bars need not be perceptible in the image over their entire width. Fundamentally, it must be possible to perceive the right edge of the left stick and the left edge of the right stick. By correlating the spacing or distance known from the reactor configuration, the spacing of the rods from each other can then be used to calculate the diameter.

According to another embodiment, the measuring device B comprises an arithmetic unit, the diameter being determined from the parameters of the deposition process captured by the arithmetic unit.

These parameters may include one or more parameters selected from the group consisting of: the volume flow rate of the reaction gas, the deposition temperature, the rod current intensity, the rod voltage, the rod resistance and the treatment time.

The volumetric flow rate may be determined, for example, by a flow meter (e.g., a suspension flow meter) in the line supplying the reaction gas to the reactor. The determination is optionally made before the feed line branches to feed multiple nozzles.

The rod current is the current used to heat the silicon rod pair (joule heating). The rod voltage is a voltage that exists between a pair of rods to generate a rod current. The voltage and amperage can be measured by commercial measuring instruments. The rod resistance is the heating resistance of the silicon rod. It is calculated from the rod voltage and current intensity. The processing time is the time that has elapsed since the start of vapor deposition.

Said one or more measured parameters are notably passed to and captured by an arithmetic unit; the rod diameter can be calculated by software. For this purpose, the diameter is usually determined by means of the camera of the measuring device B at a defined deposition time, in particular at the beginning of the deposition. The software can then use the parameters determined above to calculate the rod diameter from the deposition time using the comparison data in the previous deposition process.

The measuring device B may preferably comprise a camera and an arithmetic unit. The rod diameter can then be determined by both techniques and the values obtained can be compared with each other. In this way, the risk of measurement errors can be minimized.

Preferably, the diameter of at least two, more particularly three or four silicon rods is determined. The focal length of the camera is adjusted, for example, such that two or more silicon rods (see description above) can be seen in the generated image, whereby different diameters can be determined with one camera.

However, it is also possible to determine the diameter of different rods according to the above description using two or more cameras positioned differently around the reactor. In that case, the cameras are preferably located at different heights. It is therefore also conceivable to use two cameras arranged one above the other to determine the diameter of the same rod, despite the different heights. From the determined diameter values, an average value can be derived, which additionally increases the measurement accuracy.

According to another embodiment, the measuring device a comprises a thermal imaging system, more particularly a pyrometer or a thermal imaging camera. The measuring device a preferably comprises at least one such thermal imaging system.

Preferably, the measuring device a is positioned in such a way that the vertically extending edge of the silicon rod, the surface temperature of which is to be determined, is not outside the focal region at the end of the deposition process. The silicon rod closest to the measuring device a is preferably brought into focus with the measuring device a. Typically, this is the silicon rod closest to the observation window, the measurement device a being placed in front of the observation window. In general, the position of the viewing window or the position of the rod in the reactor plays no role in the performance of the invention as described above.

The measuring device a is usually calibrated at the beginning of the deposition process such that its measuring area is adapted in its width to the diameter of the filament rod used. The measurement region at the beginning is preferably located in the region of the center of the rod.

The measuring device a may also comprise an image processing unit for digital or analog image processing. In this way, the position of the measurement region can be checked, for example, by pixel analysis and identification of the left contour (edge) and the right contour (edge) of the silicon rod. In this respect, reference may be made to observations regarding the measurement device B.

The adaptation of the measuring area to the rods growing in diameter with the treatment time is carried out on the basis of the rod diameter determined by the measuring device B and takes place continuously or discontinuously. Preferably, this is achieved by a feedback procedure, wherein the diameter can be taken from the measuring device B before each determination of the surface temperature in the measuring area. For this purpose, the measuring devices a and B are preferably coupled to one another, in particular via a controller. The controller makes it possible to adjust the time interval, for example in the case of a discontinuous adaptation of the measurement region. Furthermore, the geometry of the measuring region and/or the extent of the measuring region can be adjusted as a function of the diameter.

The measuring region preferably has a width extending perpendicularly to the axis of the silicon rod, the measuring region being defined in terms of the diameter of the rod such that the width is between 2% and 98%, preferably between 5% and 95%, more preferably between 10% and 90% of the diameter. Due to the preferred central positioning of the measuring region (between the vertically extending edges of the silicon rod), the edge region of the silicon rod is thereby removed from the temperature capture. This improves the accuracy of the measurement, since in principle the thermal radiation in these regions can only be captured to a small extent by the detector of the thermal imaging system.

The measurement region preferably has a height extending parallel to the silicon rod axis, which is adapted in such a way that it is between 2% and 300%, preferably between 5% and 200%, more preferably between 10% and 150% of the diameter. The height of the measuring area can also be kept constant. The height of the measuring area is preferably increased to the same extent as its width.

The measuring area is preferably rectangular. The measuring region can also have a different shape. For example, it may be circular. The circle may become larger as the rod diameter increases, or as the deposition time progresses, for example, when the height is kept constant, an elliptical measurement area is formed.

According to a preferred embodiment, the surface temperature and the diameter are determined on the same silicon rod.

Preferably, two or more measuring devices a may be used to measure the surface temperature on different silicon rods.

According to another embodiment, the deposition temperature is controlled based on the surface temperature determined in the measurement area. The deposition temperature is a set point for the surface temperature, which is ideally reached at a defined point in time in the deposition process. The deposition temperature is typically between 900 and 1200 ℃ and may vary during the deposition process, for example to influence the surface properties of the silicon rod. In this context, it is important to have a surface temperature measurement technique in which the measurement results are not distorted by the extreme conditions associated with the surface. The method of the present invention represents such a technique.

Alternatively or additionally, other parameters may also be controlled depending on the measured surface temperature: such as the volume flow rate of the reactant gases, the rod amperage, the rod voltage, the rod resistance.

According to another embodiment, the deposition process is ended when the specified rod diameter is reached.

Another aspect of the invention relates to an apparatus for determining the surface temperature of at least one silicon rod in a chemical vapor deposition reactor in a deposition process, comprising a measuring device B for determining at least one diameter of the at least one silicon rod, and a measuring device a coupled to the measuring device B for determining the surface temperature in a centrally disposed measuring region disposed on the silicon rod, preferably in a centrally disposed measuring region, wherein the size and/or position of the measuring region is adapted in accordance with the determined diameter or diameters, and wherein the measuring devices a and B are placed together or independently of each other in front of an external viewing window of the reactor.

The apparatus is more particularly suitable for carrying out the aforementioned method. Thus, with regard to the design of the device, reference may be made to the above observations.

Both measuring devices a and B can be mounted rotatably, in particular perpendicularly, to the vertically extending silicon rod axis.

Preferably, the measuring devices a and B are coupled to each other via a controller. The controller may comprise, for example, computer-assisted software. The controller is preferably included in the device.

Furthermore, the device may comprise at least one analog or digital image processing unit. The image processing unit may be connected to either measuring device a or measuring device B, or both measuring devices a and B are connected to one such image processing unit.

Preferably, the controller for dynamically adapting the measurement region and the image processing unit may be co-present in one system, e.g. in software. Particularly preferably, such a system may further comprise an arithmetic unit for parametrically assisted determination of the diameter.

An important factor for the maximum error-free and reproducible temperature measurement in the measurement region is a uniform and interference-free light path. Advantageously, the viewing window and, where appropriate, all the optical elements mounted therein have a constant optical transmission. Furthermore, deposits should be prevented from depositing on the surfaces of the observation window and its elements, in particular on the surfaces facing the interior of the reactor. The high temperatures during deposition and the introduction of gases and liquids can also change the optical properties (change in light transmittance) of the viewing window and its components.

Preferably, the observation window comprises a first optical element and a second optical element, which are spaced apart from each other by a chamber filled with a cooling medium. The first optical element preferably faces the measuring device, while the second optical element faces the reactor interior. Temperature drift can be minimized by cooling. The optical element is preferably a glass or fused quartz plate. The two optical elements are preferably composed of the same material.

The cooling medium may be a liquid, more particularly water, or a gas (e.g. H)₂Or N₂). The compartment preferably has an inlet and an outlet for the cooling medium, allowing the temperature of the optical element to be kept constant by a preferably continuous flow of the cooling medium.

Preferably, the surface of the second optical element facing the interior of the reactor is filled with a gas, preferably hydrogen, in such a way that contact with the gas located inside the reactor is prevented. For this purpose, one or more nozzles blowing surfaces under a defined pressure, either continuously or at certain time intervals, may be directed at the surface inside the reactor. The one or more nozzles may also be oriented parallel to the surface so that with the continuous gas flow a protective layer is formed in front of the surface of the second optical element facing the interior of the reactor. Alternatively or additionally, there may be at least one nozzle oriented opposite the surface and displacing gas accessed from the reactor interior by the continuous gas stream.

Another aspect of the invention relates to a vapor deposition reactor for depositing polycrystalline silicon comprising a metal base plate, a detachable and coolable bell-shaped reactor shell arranged on the base plate, nozzles for supplying gas and openings for removing reaction gas, an electrode holder for a filament rod and the above-mentioned apparatus. The reactor is particularly suitable for carrying out the process of the invention.

Fig. 1 schematically shows an apparatus for carrying out the method of the invention.

Fig. 2 shows a dynamic measurement region arranged on a silicon rod.

Fig. 3 shows the region of the viewing window of an apparatus for carrying out the method according to the invention.

Fig. 1 shows a schematic cross-sectional view of a Siemens reactor 1, which comprises an apparatus 10 for determining the surface temperature of a silicon rod 3. The reactor 1 comprises a shell 2, the shell 2 enclosing a reactor interior 4. The cooling system of the reactor shell 2 is not shown. Two

observation windows

6, 8 are provided in the housing 2 at the same height. In front of the observation window 6 there is a measuring device a, which is a pyrometer. In front of the observation window 8 there is a measuring device B, which is a digital camera. Both measuring devices a and B are also coupled to a system 9, which system 9 comprises an image processing unit, a controller for dynamically adapting the temperature measurement area 7, and an arithmetic unit for determining the diameter by means of process parameters. The system 9 is a software-assisted process control station. The measuring devices a and B, the

observation windows

6, 8 and the system 9 form an apparatus 10.

In order to determine the surface temperature in the measuring region 7 on the silicon rod 3 by means of the measuring device a, the measuring device B first determines the diameter of the two

silicon rods

3, 5. For this purpose, the measuring device B records an image of the reactor interior 4 and adjusts the focus of the camera so that both

silicon rods

3, 5 are perceivable. The measuring device B may optionally also be rotatably arranged and record an image of each

silicon rod

3, 5. The image or images obtained are transmitted to the system 9 and, by means of the integrated image processing unit, the contour of the silicon rods 3, 5 (left and right edges indicated by four dashed lines) is determined. As described above, based on the distance between the left and right edges on the image, the diameters d1 and d2 of the

silicon rods

3, 5 can be calculated. Alternatively or additionally, the diameters d1 and d2 may also be calculated by the distance a of the

silicon rods

3, 5 from one another (see description above). Optionally, additional rod diameters are determined on other silicon rods. From the obtained values, an average value is formed and transmitted to the controller. The controller then adapts the measurement zone 7 of the pyrometer to the obtained value by increasing the width of the measurement zone (indicated by the two dashed lines), as shown in fig. 2.

Fig. 2 shows a detail of two

thermographic recordings

21, 22 of a portion of a silicon rod 3, which are placed one above the other and recorded with a measuring device a (pyrometer). The recording 21 is formed at about half the total deposition time. The recording 22 is formed immediately before the end of the deposition. The lighter areas 23 correspond to an increase in the growth of polysilicon between the two

recordings

21, 22. The region a1 corresponds to the measurement region 7 defined at the beginning of the deposition for determining the surface temperature of the silicon rod 3. The width b1 of the measuring region 7, which extends substantially perpendicularly to the rod axis S, is then equal to approximately 90% of the width (diameter) of the silicon rod 3. The area a2 corresponds to the measurement area 7 at the time of recording 21. At this time, the width b2 thereof is about 80% of the width (diameter) of the silicon rod 3. The dashed arrow marked c indicates a continuous adaptation of the measuring zone width according to the rod diameter over the deposition time. This adaptation is achieved by continuously determining the diameter of one or more rods using the measuring device B (see fig. 1). The position of the measuring region 7 is adapted such that it is centered on the determined rod diameter. The height of the measuring area 7 is constant.

It is clear that the width b2 of the measuring zone 7 is only equal to about 80% of the rod diameter. Furthermore, the measuring region 7 is arranged centrally, so that the region close to the bar edge 24 is still excluded from the temperature measurement. The thermal radiation emitted by the rod surface in these edge regions can no longer be sufficiently captured by the pyrometer detector, which can distort the measurement results.

Fig. 3 shows a more detailed representation of the viewing window 6 from fig. 1. The viewing window 6 includes a first optical element 32 and a second optical element 34 disposed in the barrel 30. The bobbin 30 is connected to the reactor shell 2 and is preferably composed of the same material as the latter. The

optical elements

32, 34 are made of fused silica. Located between them is a compartment 36 provided with a gas supply line 35 and a gas removal line 37. For cooling the

optical elements

32, 34, N is set₂Or H₂A continuous flow passes through the compartment 36. The optical element 34 has a side 38 facing the reactor interior 4. Arranged parallel to the side face 38 and opposite one another are two nozzles 40 which blow hydrogen into the region 39 in front of the side face 38. Such an effect is firstlyIs to cool the side 38 and secondly to prevent contact with the silicon-containing reaction gas or particles from the reactor interior 4. Any deposits present can likewise be blown off, for which purpose the nozzle 40 can also be arranged rotatably. Furthermore, a plurality of additional nozzles 42 are provided which are arranged obliquely in the direction of the reactor interior 4 and likewise blow hydrogen into the region 39. This additionally hinders contact between the side 38 and the components from the reactor interior 4.

Claims

1. Method for determining the surface temperature of at least one silicon rod in a chemical vapor deposition reactor comprising a plurality of silicon rods during a deposition process, wherein a measuring device a determines the surface temperature in a measuring region provided on the silicon rod, a further measuring device B determines continuously or discontinuously at least one diameter of the silicon rod and at least one diameter of at least one further silicon rod arranged in the reactor, the measuring devices a and B are arranged at different positions, each in front of an observation window or in front of a common observation window outside the reactor, and the size and/or position of the measuring region is adapted depending on the determined diameter or diameters.

2. The method of claim 1, comprising the steps of:

a) determining at least one diameter of at least one silicon rod with the measuring device B;

b) defining the size and/or position of the measurement region provided on the silicon rod in accordance with the diameter determined in step a);

c) determining the surface temperature in the measurement area with the measurement device a;

d) continuously or discontinuously repeating steps a), b) and c) and continuously or discontinuously adapting the size and/or position of the measurement region as a function of the diameter of the silicon rod.

3. Method according to claim 1 or 2, characterized in that the measuring device B comprises a camera, the diameter being determined by image processing of the image of the reactor interior produced by the camera.

4. Method according to any one of the preceding claims, characterized in that the measuring device B comprises an arithmetic unit, the diameter being determined by the parameters of the deposition process captured by the arithmetic unit.

5. The method according to any one of the preceding claims, characterized in that the diameter of at least two silicon rods is determined.

6. The method according to any one of the preceding claims, characterized in that the diameter of three silicon rods is determined.

7. The method according to any one of the preceding claims, wherein the measuring device a comprises a thermal imaging system.

8. The method of claim 7, wherein the thermal imaging system is a pyrometer or a thermal imaging camera.

9. The method according to any one of the preceding claims, characterized in that the measurement region has a width extending perpendicular to the silicon rod axis, the measurement region being defined such that the width is between 2% and 98% of the diameter.

10. The method of claim 9, wherein the measurement region is defined such that the width is between 5% and 95% of the diameter.

11. The method of claim 9, wherein the measurement region is defined such that the width is between 10% and 90% of the diameter.

12. The method according to claim 9, wherein the measurement region has a height extending parallel to the silicon rod axis, the measurement region being defined such that the height is between 2% and 300% of the diameter or is constant.

13. The method according to claim 12, characterized in that the measuring area is defined such that the height is between 5% and 200% of the diameter or constant.

14. The method of claim 12, wherein the measurement area is defined such that the height is between 10% and 150% of the diameter, or is constant.

15. The method according to any of the preceding claims, characterized in that the measuring area is rectangular.

16. The method according to any of the preceding claims, characterized in that the deposition temperature is controlled based on the surface temperature.

17. The method according to any of the preceding claims, characterized in that the deposition process is ended when a specified diameter is reached.

18. Reactor for depositing polycrystalline silicon, comprising a metallic base plate, a detachable and coolable bell-shaped reactor housing arranged on the base plate surrounding the reactor interior, nozzles for supplying gas and openings for removing reaction gas, an electrode holder for filament rods, and a device for determining the surface temperature of at least one silicon rod, the device comprising:

-a measuring device B for determining the diameter of at least two silicon rods arranged inside the reactor;

a measuring device A coupled to the measuring device B for determining a surface temperature in a measuring region arranged on the silicon rod;

-at least one viewing window in the reactor shell;

-a system coupled to the measuring devices A and B,

wherein the measuring devices a and B are arranged at different positions, each in front of an observation window or in front of a common observation window outside the reactor.

19. A reactor according to claim 18, wherein the viewing window comprises a first optical element and a second optical element, the optical elements being spaced apart from each other by a chamber filled with a cooling medium.

20. A reactor according to claim 19, wherein the surface of the second optical element facing the interior of the reactor is gas-filled.

21. The reactor of any one of claims 18 to 20, wherein the system is a software-assisted process control station.